once every other day during your fertile week is recommended. it allows sperm to recover. My hubby and i had sex twice during our fertile week (day before and the day after ovulation because I was using opks and knew what day I ovulated) and we are now almost 31wks!

Once per day is enough. I've read and had my doctor recommend that sex every other day leading up to fertile period, and then every day during fertile period. Any more than that is not only unnecessary, it can actually decrease sperm count per ejaculation.